1. Field of the Invention
The present invention pertains to high strength reactive materials and methods for their production, especially high strength materials having maximum stresses and strains that exceed those heretofore obtained with conventionally fabricated energetic materials. The present invention also relates to warheads comprising the high strength energetic materials.
2. Description of the Related Art
Various military warheads are equipped with a liner or inner sheath comprised of a reactive material. In principle, upon impact these warheads are intended to deliver kinetic energy and chemical energy from the reactive material. The reactive material is intended to fragment, react and release energy (chemical) as a result of the high temperature and pressure (shear) when the warhead impacts its target. The reactive fragments provide additional means for threat destruction.
At present, however, there has been a need for a sufficiently robust reactive material that is inert during storage, but which has significantly improved strength characteristics. Reactive materials produced by conventional methods have been found to possess inadequate tensile strength and to be characterized by poor elongation at break.
It would be a significant advancement in the art to discover a reactive material comprised of a fluoropolymer and a particulate metal or metalloid which has a tensile strength greater than 1800 psi and a strain (elongation at break) of greater than 30%, and a method for its production.
Metallic particles such as aluminum, zirconium, titanium, and magnesium are energetic fuels that, if distributed in a fluoropolymer, would establish an excellent reactive material. However, known methods of distributing metal particles into fluoropolymers involve the oxidization of these particles, which significantly reduces their energetic capacities. For example, U.S. Pat. No. 2,961,712 to Davis discloses a method of making filled polytetrafluoroethylene products in which metallic filler, such as aluminum powder, is inter-dispersed and precipitated in a dispersion of the polytetrafluoroethylene, which is then dried and sintered. The sintered mixture is broken up into powder. The sintered powder is then mixed with another polytetrafluoroethylene dispersion, precipitated, and subjected to a second sintering process. Davis characterizes its fillers as substantially inert, most probably due to the use of an oxidizing atmosphere during preparation and sintering of its energetic particles. Other U.S. patents disclose the use of water or aqueous solutions for dispersing metal and metalloid particles in a fluoropolymer. However, water generally functions as an oxidizing agent, and in the presence of some metals, such as aluminum, can cause the release of hazardous amounts of hydrogen gas.
It is therefore one of the objects of this invention to provide a method of making a sintered reactive material comprising non-oxidized reactive fuel particles present in a sintered fluoropolymer matrix.
It is another object of the invention to provide a sintered reactive material comprising non-oxidized reactive fuel particles in a sintered fluoropolymer matrix.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations pointed out in the appended claims.
To achieve the foregoing objects, and in accordance with the purposes of the invention as embodied and broadly described herein, a method is provided for making a sintered reactive material. The method comprises blending fuel particles and a polymer matrix comprising at least one fluoropolymer in an inert organic media to disperse the fuel particles in the polymer matrix and form a reactive material. Non-oxidized reactive metals and/or metalloids may be selected as the fuel particles. The reactive material is dried and pressed to obtain a shaped pre-form, which is sintered in an inert atmosphere to form the sintered reactive material. By sintering in an inert atmosphere, oxidation of the fuel particles is avoided.
In accordance with another aspect of this invention, there is provided a sintered reactive material comprising a matrix of one or more fluoropolymers and at least one metal or metalloid in fine particulate form dispersed in the matrix. The sintered reactive material has a tensile strength in excess of 1800 psi and an elongation at break in excess of 30%. It has been found that the sintered reactive material may exhibit tensile strengths in excess of 2700 psi and an elongation at break in excess of 100%.
The present invention also includes process embodiments which now enable the fabrication of reactive material having the sought after physical properties. The reactive materials can be shaped to form liners or inserts for warheads on various hardware, such as air-to-air, ground-to-air, or air-to-ground advanced tactical missiles. A warhead with such a liner and the missile carrying it is part of the invention.
The reactive materials can also be shaped in spheres or other selected form to generate reactive xe2x80x9cgrapexe2x80x9d shot. When a warhead impacts or an explosive is set off, the reactive material may be fragged but is nonetheless dispersed following impact or in the explosion. The pre-shaped reactive material can thus form a non-continuous liner for warhead.
The present invention also contemplates a method of protecting aircraft, ships vehicles, missiles or the like, against threats, this method comprises deploying tactical munitions or tactical missiles with the reactive material as a warhead liner or reactive material as xe2x80x9cgrapexe2x80x9d shot against the threat.